Netdata database can be queried with /api/v1/data and /api/v1/badge.svg REST API methods.

Every data query accepts the following parameters:

name

required

description

chart

yes

The chart to be queried.

points

no

The number of points to be returned. Netdata can reduce number of points by applying query grouping methods. If not given, the result will have the same granularity as the database (although this relates to gtime).

before

no

The absolute timestamp or the relative (to now) time the query should finish evaluating data. If not given, it defaults to the timestamp of the latest point in the database.

after

no

The absolute timestamp or the relative (to before) time the query should start evaluating data. if not given, it defaults to the timestamp of the oldest point in the database.

group

no

The grouping method to use when reducing the points the database has. If not given, it defaults to average.

gtime

no

A resampling period to change the units of the metrics (i.e. setting this to 60 will convert per second metrics to per minute. If not given it defaults to granularity of the database.

options

no

A bitmap of options that can affect the operation of the query. Only 2 options are used by the query engine: unaligned and percentage. All the other options are used by the output formatters. The default is to return aligned data.

dimensions

no

A simple pattern to filter the dimensions to be queried. The default is to return all the dimensions of the chart.

Database points grouping is applied when the caller requests a time-frame to be
expressed with fewer points, compared to what is available at the database.

There are 2 uses that enable this feature:

The caller requests a specific number of points to be returned.

For example, for a time-frame of 10 minutes, the database has 600 points (1/sec),
while the caller requested these 10 minutes to be expressed in 200 points.

This feature is used by netdata dashboards when you zoom-out the charts.
The dashboard is requesting the number of points the user’s screen has.
This saves bandwidth and speeds up the browser (fewer points to evaluate for drawing the charts).

The caller requests a re-sampling of the database, by setting gtime to any value
above the granularity of the chart.

For example, the chart’s units is requests/sec and caller wants requests/min.

Using points and gtime the query engine tries to find a best fit for database-points
vs result-points (we call this ratio group points). It always tries to keep group points
an integer. Keep in mind the query engine may shift after if required. See also the example.

To execute the query, the engine evaluates all dimensions of the chart, one after another.

The engine does not evaluate dimensions that do not match the simple pattern
given at the dimensions parameter, except when options=percentage is given (this option
requires all the dimensions to be evaluated to find the percentage of each dimension vs to chart
total).

For each dimension, it starts evaluating values starting at after (not inclusive) towardsbefore (inclusive).

For each value it calls the grouping method given with the &group= query parameter
(the default is average).

When netdata is reducing metrics, it tries to return always the same boundaries. So, if we want 10s averages, it will always return points starting at a unix timestamp % 10 = 0.

Let’s see why this is needed, by looking at the error case.

Assume we have 5 points:

time

value

00:01

1

00:02

2

00:03

3

00:04

4

00:05

5

At 00:04 you ask for 2 points for 4 seconds in the past. So group = 2. netdata would return:

point

time

value

1

00:01 - 00:02

1.5

2

00:03 - 00:04

3.5

A second later the chart is to be refreshed, and makes again the same request at 00:05. These are the points that would have been returned:

point

time

value

1

00:02 - 00:03

2.5

2

00:04 - 00:05

4.5

Wait a moment! The chart was shifted just one point and it changed value! Point 2 was 3.5 and when shifted to point 1 is 2.5! If you see this in a chart, it’s a mess. The charts change shape constantly.

For this reason, netdata always aligns the data it returns to the group.

When you request points=1, netdata understands that you need 1 point for the whole database, so group = 3600. Then it tries to find the starting point which would be timestamp % 3600 = 0 Within a database of 3600 seconds, there is one such point for sure. Then it tries to find the average of 3600 points. But, most probably it will not find 3600 of them (for just 1 out of 3600 seconds this query will return something).

So, the proper way to query the database is to also set at least after. The following call will returns 1 point for the last complete 10-second duration (it starts at timestamp % 10 = 0):

When you keep calling this URL, you will see that it returns one new value every 10 seconds, and the timestamp always ends with zero. Similarly, if you say points=1&after=-5 it will always return timestamps ending with 0 or 5.